netdev - Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

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Message-ID: <m1k4tzwx8z.fsf@fess.ebiederm.org>
Date:	Fri, 26 Feb 2010 12:35:56 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Daniel Lezcano <daniel.lezcano@...e.fr>
Cc:	hadi@...erus.ca, Linux Netdev List <netdev@...r.kernel.org>,
	containers@...ts.linux-foundation.org,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>,
	Ben Greear <greearb@...delatech.com>,
	Daniel Lezcano <dlezcano@...ibm.com>
Subject: Re: [RFC][PATCH] ns: Syscalls for better namespace sharing control.

> No, the plan is only one namespace at a time.

Looking at this a bit more I am frustrated and relieved.

I was looking at what it would take to join an arbitrary mount
namespace and I realized it is completely non-obvious what fs->root
and fs->pwd should be set to.

If I leave them untouched the new mount namespace is useless,
as all path lookups will give results in a different mount namespace,
so not even mount or umount can be used.

I can not change fs->root to mnt_ns->root as that is rootfs and there
is always something mounted on top so I can not use that.

In comparison an unshare of the mount namespace doesn't have to move
fs->root or fs->pwd at all and only has to update their mounts to
the corresponding mounts in the new mount namespace.

I might be able to find the topmost root filesystem and put at least
root there, but I'm not particularly fond of that option.

Eric

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